1. Field of the Invention
The present invention relates to an optical element holding apparatus, an exposure apparatus including the optical element holding apparatus, and a device manufacturing method using the exposure apparatus.
2. Description of the Related Art
An exposure apparatus can be used in a manufacturing process of a semiconductor element or other device. As discussed in Japanese Patent Application Laid-open No. 58-033255 (corresponding to U.S. Pat. No. 4,408,874), a conventional mechanism for deforming a mirror can be used to correct the astigmatism of the mirror when caused by the exposure.
Furthermore, as discussed in Japanese Patent Application Laid-open No. 2000-031039 (corresponding to U.S. Patent Application Publication No. US 2004/0144915 A1), there is another conventional method for not only deforming a mirror but also correcting a rigid-body position of the mirror in six degrees of freedom.
The system discussed in Japanese Patent Application Laid-open No. 2000-031039 includes a rigid-body servo mechanism equipped with at least three force actuators and a mirror deforming mechanism equipped with plural force actuators having no servo mechanism.
Furthermore, as discussed in Japanese Patent Application Laid-open No. 2003-203860 (corresponding to U.S. Patent Application Publication No. US 2003/0197914 A1), a force exerted between a reaction mass and an optical element can be used to adjust the position of an optical element in multiple degrees of freedom.
The system discussed in Japanese Patent Application Laid-open No. 2003-203860 further includes a correction mechanism for correcting local mirror surface imperfections (local defects or imperfections of the mirror surface), which includes a plurality of local position control loops constituted by sensors and actuators.
However, the technique discussed in Japanese Patent Application Laid-open No. 2000-031039 has the following features.
(1) Both the deforming actuators and the rigid-body position correcting actuators are force actuators having lower rigidity. Therefore, if a disturbance of lower-frequency vibrations is applied on the mirror, a large positional deviation will arise and the accuracy will deteriorate.
(2) As the actuators are required to support the gravity of a mirror, a great amount of heat is generated in the actuators.
On the other hand, the technique discussed in Japanese Patent Application Laid-open No. 2003-203860 requires plural local position control loops constituted by numerous sensors and actuators for correcting local deformations of the mirror and accordingly has the following feature.
(1) A number of position sensors are required, which corresponds to deforming actuators. Therefore, the system arrangement is complicated and causes an increase in cost.